In the field of foods, prevention of quality decline due to oxidation caused by oxygen and water vapor passing through the packaging material has been required to thereby prevent deterioration of the fat/oil and proteins. In the field of medical supplies and medicine, quality change and deterioration of the content in the package should be prevented at an even higher level. Packaging materials including an aluminum foil or an aluminum vapor deposition film have been used for the packaging material in such field. Use of such materials, however, has become problematic due to the adverse environmental effects associated with the discarding of such materials.
In view of such situation, a wide attention is being given to a silicon oxide vapor deposition film comprising a polymer film having silicon oxide formed thereon by vapor deposition, as a packaging material having a high gas barrier property which is not associated with any particular problem in the course of incineration. This silicon oxide vapor deposition film having excellent gas barrier properties is produced by evaporating a silicon oxide evaporation source by resistance heating, electron-beam heating, or the like to thereby evaporate the silicon oxide and deposit the silicon oxide vapor deposition film on the film substrate.
The silicon oxide which is used for the evaporation source has been produced by various methods. For example, JP-A 9-110412 discloses a method in which the silicon oxide is produced by depositing the silicon oxide on a surface-roughened metal substrate. JP-A 2002-97567 discloses a silicon monoxide material having an average bulk density of at least 2.0 g/cm3 and a Vickers hardness of at least 500 as well as its production method. These prior art technologies are respectively an attempt to prevent formation of pin holes on the film caused by a “splash” (splashing of the material in the heating) which had been the problem associated with the vapor deposition of the silicon oxide.
However, while these conventional methods have been effective in reducing the degree of splash, and hence, in reducing the defects such as pinholes formed on the film, such improvement has still been insufficient, and the inventors believe that there is still room for further improvements. More specifically, the silicon oxide produced by such conventional technology had mainly been the one produced by precipitating the silicon oxide vapor on the substrate and peeling the deposited silicon oxide from the substrate, and accordingly, inconsistent in shape, size, thickness, and other physical properties. Use of such material for the evaporation source resulted in the considerable lot-to-lot variation in the course of the vapor deposition, and stable reduction of the splash was difficult. In addition, insufficient strength of the silicon oxide often resulted in the generation of fine powder, and this powder often caused the splash.